This relates generally to displays, and, more particularly, to displays that include protective layers that prevent the operation of the display from being disrupted from electric fields.
Displays are widely used in electronic devices to display images. Displays such as liquid crystal displays display images by controlling liquid crystal material associated with an array of image pixels. A typical liquid crystal display has a color filter layer and a thin film transistor layer formed between polarizer layers. The color filter layer has an array of pixels each of which includes color filter subpixels of different colors. The thin film transistor layer contains an array of thin film transistor circuits. The thin film transistor circuits can be adjusted individually for each subpixel to control the amount of light that is produced by that subpixel pixel. A light source such as a backlight may be used to produce light that travels through each of the layers of the display.
A layer of liquid crystal material is interposed between the color filter layer and the thin film transistor layer. During operation, the circuitry of the thin film transistor layer applies signals to an array of electrodes in the thin film transistor layer. These signals produce electric fields in the liquid crystal layer. The electric fields control the orientation of liquid crystal material in the liquid crystal layer and change how the liquid crystal material affects polarized light.
An upper polarizer is formed on top of the display and a lower polarizer is formed on the bottom of the display. As light travels through the display, the adjustments that are made to the electric fields in the liquid crystal layer are used to control the image that is displayed on the display.
In many electronic devices, it is desirable to incorporate touch screen functionality into a display. Touch screens can be used to provide a device with a touch interface. A touch interface may allow users to interact with a device through on-screen touch commands such as finger taps and swipes.
A typical touch screen includes a touch panel with an array of touch sensor electrodes. Touch sensor processing circuits can measure capacitance changes on the touch sensor electrodes to determine the position at which a user's finger is contacting the touch array.
When an external object such as a user's finger comes into contact with a display, there is a potential for electrostatic charges on the user's finger to create large electric fields in the display. These electric fields may disrupt the operation of the display. For example, the electric fields from an electrostatic charge may interfere with the electric fields created by the electrodes of the thin-film-transistor layer. This can create spots or other visual artifacts on the screen.
In some liquid crystal displays that include touch panels, the touch panel may be located above the liquid crystal layer. In this type of situation, the electrodes of the touch sensor array may prevent charge-induced electric fields from reaching the liquid crystal layer.
It may sometimes be desirable to construct a display with different touch sensor configurations. For example, it may be desirable to incorporate a touch sensor electrodes into a display at a location that is below the liquid crystal layer. This type of display is sometimes referred to as an in-cell display. If care is not taken, however, the display will be susceptible to disruptions from electrostatic charge, because the touch sensor electrodes will not prevent charge-induced electric fields from reaching the liquid crystal layer.
It would therefore be desirable to provide displays such as liquid crystal displays that have improved electric field shielding layers.